Amby Purfoot

EXERCISE – even light activity such as vacuuming or walking the dog – is even healthier than previously believed.

Two recent mortality studies are among the first wave of epidemiological papers based on objective measures of physical activity, rather than self-reported responses. As such, they are more accurate.

The new investigations were performed by researchers at Harvard University and the renowned Karolinska Institute in Stockholm. They found the most active subjects had a 50% to 70% decline in mortality during a defined follow-up period compared to the least active participants. Previous self-report research had pegged this benefit at about 20% to 35%.

“We were somewhat surprised by the strong association between light activity and mortality,” said Ing-Mari Dohrn, first author of the Swedish paper. “It was a strong factor for reductions in cancer and cardiovascular deaths, as well as for all-cause mortality.”

Diet and exercise studies have long been troubled by reliance on self-reporting, which is notoriously inaccurate. But now there are lightweight, wearable accelerometers (think Fitbit) that allow scientists to collect objective activity data, such as how much they sit and move.

The Harvard researchers mailed accelerometers to more than 16 000 US women, who wore them for 15 hours a day on four or more days. The researchers then followed the women for an average of 2.3 years to determine their mortality data. The Swedes gave similar devices to 851 subjects who wore them for 14 or more hours on four or more days. These subjects were tracked for 14.2 years.

The two studies agreed – subjects who moved a lot enjoyed a substantial longevity benefit over those who moved little. “Our most active women had a 60% to 70% decline in mortality, which compares favourably to the 50% difference you would see between non-smokers and smokers.”

The Swedish team found that individuals who sit fewer than six hours a day have a 66% lower mortality risk than those who sit more than 10 hours a day.

Few adults engage in a large amount of moderate to vigorous activity, but those minutes give a big boost to health and longevity. “The message should remain – 30 minutes